The present invention relates generally to automatic gain control (AGC) in communication devices, and more particularly to the improvement of AGC feedback systems using a feed forward scheme.
AGC is a signal processing technique used to dynamically compensate for widely-varying channel gains encountered in various wireless and wire-line media at the receiver end. The strength of the wanted signal fluctuates because of changes in propagation conditions. Such conditions include the distance between transmitter and receiver, traveling medium such as air, wire or fiber optics, and the ambient noise around the medium. A receiver therefore includes AGC to maintain the signal at the input to a detector at a constant value despite fluctuations in the signal strength of the antenna or receiver. In a traditional approach, the AGC block forms a loop by estimating the received signal strength at an output by using a peak detector. The AGC adjusts the gain, negatively or positively, so as to bring the further received signal strength to a specified target peak value.
The process of adjusting the gain for incoming signals by processing older signals has its disadvantages. While the signal is being processed, a delay is introduced. This delay could severely affect newer incoming signals. Such delays could also render incoming data erroneous, as the gain for the incoming signal might be too much or too little. Additionally, if the peaks of incoming signals vary rapidly within a given period, the delay of the AGC might completely miss the erratic signal and thus make the data incorrect. Given that digital communications typically require a fast transfer rate, the problem described above is critical and must be promptly addressed.
Desirable in the art of automatic gain control designs are additional designs that provide a gain compensation mechanism to thereby reduce or eliminate the possibility of erroneous data detection.